5R55S Transmission Rebuild - Taking It To The Next Level

Level 10 rebuilds a 5R55S after years of abuse behind a supercharged ’06 Mustang GT

Michael Galimi

April 4, 2011

Ford rolled out a completely new Mustang in 2005 with stellar looks, an outstanding engine package, and a new automatic transmission that impressed even diehard stick-shift guys. We instantly saw people throwing tunes in the ECU and adding nitrous, cold-air kits, exhaust systems, turbo kits, and supercharger systems.

The quest for more power pushed the aftermarket into overload, and now we’re left with a skewed sense of reality as 500 rwhp from stock engines is expected every time a wrench is spun. The 4.6L Mustang Three-Valve engine program lasted six years, and we can confidently point to the supercharger as being one of the most popular upgrades. Going mid-11s is as simple as a blower, custom tune, and sticky tires.

Anthony Giagnacovo can certainly attest to the simplicity of it all. His ’06 Mustang GT benefits from a Saleen twin-screw supercharger (10 psi), JDM Engineering tune, Kook’s headers/ X-style midpipe/axle-back exhaust, and 17-inch Mickey Thompson drag radials. The car was modified in 2008 with just 5,000 miles on the ticker.

Once the mods were done, Giagnacovo wasn’t shy about racing the car hard, as he attends three NMRA events a year, plus local Mustang events at Englishtown and Atco Raceway, countless test-and-tune sessions, as well as a lot of cruising at the Jersey Shoreyes, we said the Jersey Shore. Best time to date has been an 11.24 at 120 mph, and the car cranks out 469 rwhp through the automatic transmission that is relatively untouched. He added a hardened input shaft and trans cooler, otherwise, the transmission is the same as it rolled off the assembly line--including the torque converter.

All too often we proudly display performance gains on these pages, but rarely do we speak of long-term endurance of the parts. Unfortunately, it is just too hard to track the progress of each install, and every owner treats his or her equipment differently. For Giagnacovo, it took 25,000 miles and who-knows-how-many dragstrip runs, but the stock trans threw up the white flag and surrendered. The car wouldn’t move, so JDM Engineering yanked it out and sent the 5R55S to Level 10 Performance Transmission in Hamburg, New Jersey. He smoked Second, Third, Fourth, and Fifth gears, comments Pat Barrett of Level 10.

The company isn’t a stranger to the pages of MM&FF, as it was responsible for delivering a bulletproof 4R100 transmission for our former project vehicle, The Fridge, a low-10-second Gen 2 Lightning that was driven daily and whipped often. Barrett and his Level 10 shop did the same thing to Giagnacovo’s trans since more dragstrip abuse and street fun are on the agenda.

Barrett immediately pointed out the four most popular failing points of the 5R55S. The first is an issue with the input shaft--it will bend and snap under hard use, including some aftermarket ones. "The shaft can break two ways, locking the torque converter up at the wrong time, or from excessive wheelhop," states Barrett. "The input shaft was never designed to lock up under WOT, but you know racers--they love to get the mph out the car by locking it up. Our shaft is designed to withstand that abuse. The wheelhop will shake the shaft and snap."

The next issue on the list is a cold start valve failure. According to Barrett, there is a special circuit in the valvebody that restricts fluid flow to and from the trans cooler. This is done to bring the trans up to operating temperature quickly.

It was designed for extreme cold weather startups, like 20-30 below zero. In a perfect world this valve works perfectly, but we don’t live in a perfect world, adds Barrett. Level 10’s overhaul eliminates the valve to prevent any problems because 99 percent of these cars aren’t going to be fired up in that extreme weather.

Photo Gallery

Level 10 addresses a third issue regarding line pressure that is controlled by the electronic solenoid. According to Barrett, there are 30 (computer written) lines of programming for line pressure and transmission functions in tuning software like the SCT products he uses. He said not every tuner modifies the trans functions properly. The solenoid is cranked up manually to eliminate any tuner problems. Level 10 raises the line pressure from 90 psi to 180 for proper operation in high-performance applications.

The final issue is the Overdrive and Intermediate servo bores in the case. The factory case is made from a weak aluminum, states Barrett. He went on to tell us that the bores become distorted and leak fluid past the servos. The servos control the line pressure for the Intermediate and Overdrive bands inside the transmission. It makes tuning the line pressure inconsistent, since there is no way to accurately know what effect the servo leakage has on it. Because of this, the servo bores are modified and an insert is installed to prevent the distortion. This will make the servo actuation consistent and predictable so the transmission tune can be properly adjusted.

On top of those modifications, Level 10 added the usual upgraded parts, like better clutches and bands, and it does an overall inspection of the major components. Once completed, the 5R55S was ready for a long service life on the street and strip.

Photo Gallery

Giagnacovo is ruthless on the car as two of the three NMRA events he attends each year are far from his home state of New Jersey. It brings reliability to a whole new level when you drive your race car to the races. His routine includes tossing his luggage and a pair of Mickey Thompson drag radials (mounted on stock Bullitt wheels) in the trunk and hitting the road. Its best time (11.24 at 120 mph) came last year when Giagnacovo drove the Stang to Bradenton, Florida, for the NMRA Spring Break Shootout, where he competed in the JDM Super Stang category. The Florida race is nearly 20 hours from his home, yet he didn’t think twice about making the journey sans truck and trailer.

JDM Engineering re-installed the transmission and Giagnacovo is happy to report it shifts nicely, and the new Level 10 torque converter (approximately 2,600-rpm stall speed) is barely noticeable on the street, but is effective when he jumps on the loud pedal. The final test came in March, when he drove from New Jersey to Bradenton, Florida, to compete in the NMRA season opener. Although he lost early, the vehicle ran strong and withstood the racing, as well as the 1,500-mile trip.

Filling Up the 5R55S

Level 10 recommends Mercon 5 fluid only, and the transmission takes 9.5 quarts. Barrett warns that the transmission is sensitive to the fluid level. A special fill tube (available from Snap-On, Matco, and others) screws into the transmission pan, and a hand pump like the one shown is required. Barrett recommends pumping in six quarts before starting the vehicle. Once the six quarts are in, start up the engine, run the shifter through each gear, put it into Neutral, and pump in the remainder of the fluid. There is no dipstick on these transmissions. You’ll know when it’s full when you pull out the fill tube and the pan just drips a little bit of oil, notes Barrett. He finished with one more tipfill the transmission when the fluid is 180 degrees. If filled cold, then fluid will push out of the vent.